Generally speaking, an information system comprises a storage apparatus equipped, for example, with multiple HDDs (hard disk drives) as storage devices, and a storage system including one or more such storage apparatuses is accessed from a plurality of higher-level devices (for example, host computers) via a Storage Area Network (SAN). A storage apparatus provides reliability, which exceeds the reliability of an independent HDD, by adopting a method of realizing the enhancement of reliability according to the RAID (Redundant Array of Independent (or Inexpensive) Disks) technology. Nevertheless, when a natural disaster such as a massive earthquake, tsunami or typhoon occurs, there is a possibility that the storage apparatus itself cannot be recovered. In the foregoing case, the availability (server continuity) of the information system cannot be satisfied only with the reliability of the foregoing RAID. For example, since there will be a significant impact on the economic activities if financial institutions discontinue their services, demanded is a technology for creating a backup in a remote location in preparation for disasters or the like.
As a high-availability technique to deal with this kind of situation, PTL 1 discloses a configuration of performing a remote copy between a local site including a first storage apparatus and a second storage apparatus, and a remote site including a third storage apparatus and a fourth storage apparatus. The host computer sends a read/write request to the first storage apparatus. The second storage apparatus is a backup of the first storage apparatus and, when a failure occurs in the first storage apparatus, business affairs are continued by the second storage apparatus performing a failover.
Here, when a configuration is adopted where the same identifier is assigned to two storage apparatuses; for example, a storage apparatus A and a storage apparatus B, and the storage apparatus A provides a virtual volume A corresponding to the physical volume A to a host computer, and the storage apparatus B provides a virtual volume B, which corresponds to the physical volume B and has the same identifier as the virtual volume A, to a host computer, a host computer comprising a general alternate path function will recognize the physical volumes in the respective storage apparatuses as one virtual volume.
In this configuration, the host computer can access (read from/write into) both storage apparatuses. Consequently, the access load can be balanced between the two storage apparatuses while maintaining the redundancy.
In order to realize this function, it is necessary to synchronize the data between the two physical volumes. Thus, in write processing, since writing will be complete after data is written into two physical volumes, much time is required for the response. Thus, in business affairs that lay importance on response performance, the distance between the physical volumes needs to be a relatively short distance. Thus, in the occurrence of a widespread disaster, there is a possibility that the two storage apparatuses may both become unavailable. Thus, in order to increase the service continuity, it is necessary to have a backup in a long-distance data center based on remote copy.